As a technique for accurately estimating a sound source direction without depending on the distance from a sound source to a microphone, there is a technique that utilizes a phase difference distribution generated from acoustic signals of a plurality of channels. The phase difference distribution is a distribution representing phase differences for individual frequencies of the acoustic signals of a plurality of channels, and has a specific pattern dependent on the direction of a sound source in accordance with the distance between the microphones collecting a sound from the acoustic signals of the plurality of channels. This pattern is unchanged even when the sound pressure level difference of the acoustic signals of the plurality of channels is small. For this reason, even when a sound source is located away from microphones causing a sound pressure level difference of acoustic signals of a plurality of channels to be small, the use of a phase difference distribution enables the direction of a sound source to be accurately estimated.
However, in the conventional technology of estimating the direction of a sound source using a phase difference distribution, the calculation amount required for the processing of obtaining a direction from a phase difference distribution is large, thereby inhibiting the direction of a sound source from being estimated in real time with equipment having low calculation capacity. For this reason, it is demanded that estimation of a sound source direction using a phase difference distribution be performed in a low calculation amount.